Biology subjects

Polissi, A.

Publications and source records attributed to Polissi, A..

4 recordsLinked to original sources

bioRxiv2025

A novel peptidoglycan deacetylase modulates daughter cell separation in E. coli

Peptidoglycan hydrolases facilitate bacterial cell wall growth by creating space for insertion of new material and allowing physical separation of daughter cells. In Escherichia coli, three peptidoglycan amidases, AmiA, AmiB and AmiC, cleave septal peptidoglycan during cell division. The LytM-domain proteins EnvC and NlpD activate these amidases either from inside the cell or the outer membrane: EnvC binds to the cytoplasmic membrane-anchored divisome components FtsEX, and NlpD and ActS are outer membrane lipoproteins. Here we report the identification of a novel periplasmic deacetylase called SddA that removes acetyl groups from denuded peptidoglycan glycan strands, the products of amidases. SddA is a substrate for the periplasmic protease Prc, suggesting regulation via protein degradation. The sddA gene is co-expressed with the gene encoding EnvC, linking SddA function to amidase activation. Consistent with this link, the deletion of sddA alleviates phenotypes associated with lack of amidase activation, while overexpression of sddA alleviates phenotypes related to a defective Tol-Pal system and causes cell chaining due to reduced septum peptidoglycan cleavage unless envC is co-expressed. We present a model according to which SddA modulates the activation of the septum-splitting amidases during cell division. AUTHOR SUMMARYBacteria surround their cell membrane by the essential peptidoglycan (cell wall) layer to prevent bursting open due to their turgor. During cell division, bacteria produce a septum at midcell, which must be cleaved for daughter cells to separate. Here, we report the identification of a new enzyme, SddA, that modifies a particular type of peptidoglycan material, denuded glycan chains released during the splitting of septal peptidoglycan for daughter cell separation, in the Gram-negative Escherichia coli. We propose a model in which SddA modulates a switch in the septal peptidoglycan splitting, ensuring splitting is activated from the cell membrane in the early stages of cell division and from the outer membrane in the late stages.

microbiology↗

bioRxiv2024

Mechanoreceptors initiate innate immunity in response to microbial infections

How mammals mount an effective immune response against infectious agents remains an unresolved fundamental issue in biology. Here, we discovered an unforeseen two-tier mechanism of neutrophil recruitment during infections, in which mechanosensing is key to initiating innate immunity. Leveraging a skin infection model and pathogenic bacteria and fungi, we demonstrate that the early recruitment of neutrophils is mainly danger-driven and partly reminiscent of sterile inflammation. Mechanistically, neutrophil recruitment is initiated by a mechanosensor-dependent pathway, involving the activation of PIEZO1 channels. This leads to LTB4 production, which, along with IL-1, induces the release of CXCL1, promoting neutrophil arrival to the site of infection. In contrast, later neutrophil recruitment is TLR- and CXCL2-dependent, highlighting a shift towards a pathogen-driven response to sustain inflammation. These findings advance our understanding of innate immunity by uncovering that mechanical and biochemical signals integrate into a circuit that initiates innate immune responses to microbial infections.

immunology↗

bioRxiv2021

LptB2FG is an ABC transporter with Adenylate Kinase activity regulated by LptC/A recruitment

Lipopolysaccharide (LPS) is an essential glycolipid covering the surface of gram-negative bacteria. Its transport involves a dedicated 7 protein transporter system, the Lpt machinery, that physically spans the entire cell envelope. LptB2FG complex is an ABC transporter that hydrolyses Adenosine Triphosphate (ATP) to extract LPS from the inner membrane (IM). LptB2FG was extracted directly from IM with its original lipid environment by Styrene-Maleic acids polymers(SMA). SMA-LptB2FG in nanodiscs displays ATPase activity and a previously uncharacterized Adenylate Kinase (AK) activity. It catalyzes phosphotransfer between two ADP molecules to generate ATP and AMP. ATPase and AK activities of LptB2FG are both stimulated by the interaction on the periplasmic side with LptC and LptA partners and inhibited by the presence of LptC transmembrane helix. Isolated ATPase module (LptB) has weak AK activity in absence of LptF and LptG, and one mutation, that weakens affinity for ADP, has AK activity similar to that of fully assembled complex. LptB2FG is thus capable of producing ATP from ADP depending on the assembly of the Lpt bridge and the AK activity might be important to ensure efficient LPS transport in fully assembled Lpt system.

biochemistry↗

bioRxiv2021

DpaA detaches Braun's lipoprotein from peptidoglycan

Gram-negative bacteria have a unique cell envelope with a lipopolysaccharide-containing outer membrane that is tightly connected to a thin layer of peptidoglycan. The tight connection between the outer membrane and peptidoglycan is needed to maintain the outer membrane as an impermeable barrier for many toxic molecules and antibiotics. Enterobacteriaceae such as Escherichia coli covalently attach the abundant outer membrane-anchored lipoprotein Lpp (Brauns lipoprotein) to tripeptides in peptidoglycan, mediated by the transpeptidases LdtA, LdtB and LdtC. LdtD and LdtE are members of the same family of LD-transpeptidases but they catalyse a different reaction, the formation of 3-3 cross-links in the peptidoglycan. The function of the sixth homologue in E. coli, LdtF remains unclear, although it has been shown to become essential in cells with inhibited LPS export to the outer membrane. We now show that LdtF hydrolyses the Lpp-peptidoglycan linkage, detaching Lpp from peptidoglycan, and have renamed LdtF to peptidoglycan meso-diaminopimelic acid protein amidase A (DpaA). We show that the detachment of Lpp from peptidoglycan is beneficial for the cell under certain stress conditions and that the deletion of dpaA allows frequent transposon inactivation in the lapB (yciM) gene, whose product down-regulates lipopolysaccharide biosynthesis. DpaA-like proteins have characteristic sequence motifs and are present in many Gram-negative bacteria of which some have no Lpp, raising the possibility that DpaA has other substrates in these species. Overall, our data show that the Lpp-peptidoglycan linkage in E. coli is more dynamic than previously appreciated. IMPORTANCEGram-negative bacteria have a complex cell envelope with two membranes and a periplasm containing the peptidoglycan layer. The outer membrane is firmly connected to the peptidoglycan by highly abundant proteins. The outer membrane-anchored Brauns lipoprotein (Lpp) is the most abundant protein in E. coli and about one third of the Lpp molecules become covalently attached to tripeptides in peptidoglycan. The attachment of Lpp to peptidoglycan stabilizes the cell envelope and is crucial for the outer membrane to function as a permeability barrier for a range of toxic molecules and antibiotics. So far the attachment of Lpp to peptidoglycan has been considered to be irreversible. We have now identified an amidase, DpaA, which is capable of detaching Lpp from PG and we show that the detachment of Lpp is important under certain stress conditions. DpaA-like proteins are present in many Gram-negative bacteria and may have different substrates in these species.

microbiology↗